Error while trying to connect to open COM port - matlab

Question

I'm trying to connect to my micro controller using Matlab GUI. The first step is setting up the elements, my window consists of 4 axes, 1 popup window (to choose the com port) and 3 push buttons, "connect, "start, and stop"
I need the user to choose the COM port, which will be opened once "connect" is pressed. Here is my interface:
Here is my code :
function varargout = gui2(varargin)
% GUI2 MATLAB code for gui2.fig
% GUI2, by itself, creates a new GUI2 or raises the existing
% singleton*.
%
% H = GUI2 returns the handle to a new GUI2 or the handle to
% the existing singleton*.
%
% GUI2('CALLBACK',hObject,eventData,handles,...) calls the local
% function named CALLBACK in GUI2.M with the given input arguments.
%
% GUI2('Property','Value',...) creates a new GUI2 or raises the
% existing singleton*. Starting from the left, property value pairs are
% applied to the GUI before gui2_OpeningFcn gets called. An
% unrecognized property name or invalid value makes property application
% stop. All inputs are passed to gui2_OpeningFcn via varargin.
%
% *See GUI Options on GUIDE's Tools menu. Choose "GUI allows only one
% instance to run (singleton)".
%
% See also: GUIDE, GUIDATA, GUIHANDLES
% Edit the above text to modify the response to help gui2
% Last Modified by GUIDE v2.5 02-Mar-2017 15:10:00
% Begin initialization code - DO NOT EDIT
gui_Singleton = 1;
gui_State = struct('gui_Name', mfilename, ...
'gui_Singleton', gui_Singleton, ...
'gui_OpeningFcn', #gui2_OpeningFcn, ...
'gui_OutputFcn', #gui2_OutputFcn, ...
'gui_LayoutFcn', [] , ...
'gui_Callback', []);
if nargin && ischar(varargin{1})
gui_State.gui_Callback = str2func(varargin{1});
end
if nargout
[varargout{1:nargout}] = gui_mainfcn(gui_State, varargin{:});
else
gui_mainfcn(gui_State, varargin{:});
end
% End initialization code - DO NOT EDIT
% --- Executes just before gui2 is made visible.
function gui2_OpeningFcn(hObject, eventdata, handles, varargin)
% This function has no output args, see OutputFcn.
% hObject handle to figure
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
% varargin command line arguments to gui2 (see VARARGIN)
global comport ;
global COMnum ;
% Choose default command line output for gui2
handles.output = hObject;
% Update handles structure
guidata(hObject, handles);
% UIWAIT makes gui2 wait for user response (see UIRESUME)
% uiwait(handles.figure1);
% --- Outputs from this function are returned to the command line.
function varargout = gui2_OutputFcn(hObject, eventdata, handles)
% varargout cell array for returning output args (see VARARGOUT);
% hObject handle to figure
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
% Get default command line output from handles structure
varargout{1} = handles.output;
% --- Executes on button press in Connect1.
function Connect1_Callback(hObject, eventdata, handles)
% hObject handle to Connect1 (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
COMnum = get(handles.COM2,'String');
comport = serial(COMnum, 'BaudRate', 115200); % setup comport
comport.InputBufferSize = 500000;
flushinput(comport);
fopen(comport);
% --- Executes on button press in Start1.
function Start1_Callback(hObject, eventdata, handles)
% hObject handle to Start1 (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
% --- Executes on button press in Stop1.
function Stop1_Callback(hObject, eventdata, handles)
% hObject handle to Stop1 (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
% --- Executes on selection change in COM2.
function COM2_Callback(hObject, eventdata, handles)
% hObject handle to COM2 (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
% Hints: contents = cellstr(get(hObject,'String')) returns COM2 contents as cell array
% contents{get(hObject,'Value')} returns selected item from COM2
Com=get(handles.COM2,'string');
setappdata(0,'COM',Com);
guidata(hObject, handles);
% --- Executes during object creation, after setting all properties.
function COM2_CreateFcn(hObject, eventdata, handles)
% hObject handle to COM2 (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles empty - handles not created until after all CreateFcns called
% Hint: popupmenu controls usually have a white background on Windows.
% See ISPC and COMPUTER.
if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
set(hObject,'BackgroundColor','white');
end
My problem is that when I run this program I get the following error:
gui2
Error using serial (line 107)
Cannot create: No constructor with appropriate signature exists in Java class com.mathworks.toolbox.instrument.SerialComm
Error in gui2>Connect1_Callback (line 87)
comport = serial(COMnum, 'BaudRate', 115200); % setup comport
Error in gui_mainfcn (line 95)
feval(varargin{:});
Error in gui2 (line 42)
gui_mainfcn(gui_State, varargin{:});
Error in
matlab.graphics.internal.figfile.FigFile/read>#(hObject,eventdata)gui2('Connect1_Callback',hObject,eventdata,guidata(hObject))
Error while evaluating UIControl Callback
Why is that happening?
Thanks

Answer 1

Looking at the examples section of the documentation of uicontrol, we can see that the String property of a 'popup' (aka dropdown) holds a cell array:
% Create pop-up menu
popup = uicontrol('Style', 'popup',...
'String', {'parula','jet','hsv','hot','cool','gray'},...
'Position', [20 340 100 50],...
'Callback', #setmap);
This is why, when you're calling
COMnum = get(handles.COM2,'String');
comport = serial(COMnum, 'BaudRate', 115200); % setup comport
You're passing serial a cell array for a first argument, while it is expecting a string.
What can be done about this? The documentation tells us this as well:
The Value property stores the row indexes of currently selected list box items
For it to work you should do something like:
comport = serial(COMnum{get(handles.COM2,'Value')}, 'BaudRate', 115200);
I suggest you look into debugging - it contains useful tips that could've helped you find the problem on your own.